Rhodium-incorporated faujasite prepared at 80 °C

Rhodium-incorporated zeolites were synthesized from orthosilicate, aluminum nitrate, and rhodium chloride at 80 °C. Crystal phase diagram (zeolite types as functions of rhodium feed ratio and reaction period) showed that pure faujasite was formed in a wide range, but prolonged reaction caused partial transformation from faujasite to cancrinite at the rhodium feed ratio Rh/(Al + Rh) ≤ 0.02 and to gismondine at Rh/(Al + Rh) ≥ 0.4. X-ray diffraction analysis illustrated that an increase in the rhodium feed ratio caused appreciable decreases in the d-spacings, suggesting that rhodium was incorporated into the faujasite framework. ICP-OES analysis for the products showed that the rhodium content increased almost linearly with the increase in the rhodium feed ratio with an upper limit of the analyzed Rh content Rh/(Al + Rh) = 0.183 at the Rh feed ratio of 0.3. The products were almost quantitatively ion-exchanged using an ammonium chloride aqueous solution to study the ammonia desorption profiles on TG-DTA/MS analysis in the heating process. Considerably sharp exothermic peaks were observed at 245 °C simultaneously in the heating process. These peaks are probably related to catalytic decomposition of ammonia and desorption of ammonia, nitrogen, and water in the zeolite. A hypothesis was proposed for this mechanism: rhodium can be abruptly eliminated at an elevated temperature from the zeolite framework toward the micropores to form its hydroxides or oxides, then they triggered a catalytic decomposition of the adsorbed ammonia. The effect of calcination on crystallinity of the products and catalytic reactivity for hydrogen peroxide decomposition supported the proposed mechanism.